The nucleation and emission of dislocations from a crack tip under mode-II loading were analyzed by using a molecular dynamics method and the Finnis-Sinclair potential. A suitable atomic lattice configuration was used which permitted a complete analysis to be made of the nucleation, emission, dissociation and piling-up of dislocations. The results showed that, although pure mode-II loading was applied, the crack tip generally exhibited a combined mode. The stress distributions before dislocation-emission were in agreement with the elasticity solution, but were not so following the emission. The critical stress intensity factor which corresponded to dislocation-nucleation depended upon the loading rate. The separations of a pair of partial dislocations and the full dislocations were also dependent upon the loading rate. When the first partial dislocation was blocked, a pile-up of dislocations could be set up. It was also found that the dislocation could move at sub-sonic wave speeds (less than the shear-wave speed) or at transonic speeds (greater than the shear-wave speed but less than the longitudinal-wave speed); depending upon the loading rate. The atomic lattice broke down at the longitudinal wave speed which corresponded to a loading rate of 1.15MPavm/ps in Cu.

Simulation of Nucleation and Emission of Dislocations by Molecular Dynamics Method. Y.W.Zhang, T.C.Wang, Q.H.Tang: Journal of Applied Physics, 1995, 77[6], 2393-9